JP2000179382A - Air/fuel ratio control unit of internal combustion engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently purify toxic substances within exhaust gases, by add correcting the skip amount of the air/fuel ratio feedback correction factor to the rich side according to the correction factor at high load generated by correction factor generating means for high load operation. SOLUTION: When activation conditions for air/fuel ratio feedback control are met (S100), whether the driving state is in the high load region is judged (S102) when it is judged that an upstream side air/fuel ratio flag F1 of an upstream side oxygen sensor has reversed (S101). When it is judged to be in the high load region, a high load correction factor KRS, which calculates the add correction based on the amount of intake air, is calculated such that the air/fuel ratio feedback correction factor is on the rich side. Then, whether the upstream side air/fuel ratio flag F1 is O is judged (S104). For example, when the upstream side air/fuel ratio flag F1 is 0, the air/fuel ratio needs to be on the rich side, so air/fuel ratio feedback correction factor FAF is skip added by only the amount corresponding to the correction factor at high load KRS and the rich skip amount RS (S105).

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an air-fuel ratio control device for controlling an air-fuel ratio of an internal combustion engine.

[0002]

BACKGROUND OF THE INVENTION Single O ₂ sensor system having an oxygen sensor only on the upstream side of the exhaust purification catalyst (air-fuel ratio sensor) generating an air-fuel ratio feedback correction coefficient FAF by the output of the upstream oxygen sensor, the air The fuel injection amount is corrected by the fuel ratio feedback correction coefficient FAF to adjust the air-fuel ratio of the internal combustion engine to a desired air-fuel ratio. In a single O ₂ sensor system, when the air-fuel ratio control using the air-fuel ratio feedback correction coefficient FAF cannot be performed with high accuracy due to variations in the output of the oxygen sensor, variations due to components such as the fuel injection valve, and variations due to aging. was there.

[0003] Therefore, in order to perform more accurate air-fuel ratio control, it is disposed an oxygen sensor also downstream in addition to the upstream side of the exhaust gas purification catalyst, in some cases double O ₂ sensor system is employed. In the double O ₂ sensor system, the downstream oxygen sensor is located downstream of the exhaust purification catalyst, so it has little thermal influence, and there is little influence of poisoning by various harmful components in exhaust gas. As a result, it has a stable output characteristic and can compensate for a decrease in the accuracy of the air-fuel ratio feedback correction coefficient FAF based on the upstream oxygen sensor. Specifically, by controlling the rich skip amount and lean skip amount of the air-fuel ratio feedback correction coefficient FAF based on the output of the downstream oxygen sensor, the accuracy of the air-fuel ratio control using the air-fuel ratio feedback correction coefficient FAF is improved. ing.

[0004]

However, even in the double O ₂ sensor system, when the load is high in the air-fuel ratio feedback range, the amount of intake air and the combustion temperature increase due to the increase in the amount of intake air and the combustion temperature. Since nitrogen oxide NOx increases, it may not be possible to sufficiently purify the nitrogen oxide NOx, and further improvement has been desired.

Accordingly, an object of the present invention is to provide an air-fuel ratio control device for an internal combustion engine which can efficiently purify harmful substances in exhaust gas even at a high load in an air-fuel ratio feedback region. is there.

[0006]

SUMMARY OF THE INVENTION The present invention relates to an exhaust purification catalyst provided on an exhaust passage of an internal combustion engine, and an upstream air-fuel ratio provided upstream of the exhaust purification catalyst for detecting an air-fuel ratio of the internal combustion engine. A downstream air-fuel ratio sensor provided downstream of the exhaust purification catalyst and detecting the air-fuel ratio of the internal combustion engine; and a rich skip amount and lean air-fuel ratio feedback correction coefficient based on the output of the downstream air-fuel ratio sensor. A skip amount generating means for generating a skip amount, an air-fuel ratio feedback correction coefficient generating means for generating an air-fuel ratio feedback correction coefficient based on the skip amount generated by the skip amount generating means and an output of the upstream air-fuel ratio sensor, During a high load operation of the internal combustion engine, a high load correction coefficient for adding a rich skip amount generated by the skip amount generation means is generated. A load correction coefficient generating unit, and a skip amount updating unit that stops updating of the rich skip amount by the rich skip amount generating unit when the output of the downstream air-fuel ratio sensor is rich during high load operation of the internal combustion engine. And a stopping means.

According to the present invention, the combustion temperature is reduced by adding and correcting the skip amount of the air-fuel ratio feedback correction coefficient to the rich side by the high load correction coefficient generated by the high load correction coefficient generation means. Hydrocarbon HC and carbon monoxide CO, which are unburned fuels and serve as reducing agents for reducing and purifying nitrogen oxides NOx on the exhaust purification catalyst 2
Supply. By reacting these hydrocarbons HC and carbon monoxide CO with increasing amounts of nitrogen oxides NOx at high load in the air-fuel ratio feedback control region, harmful substances in exhaust gas can be reliably purified. .

When the exhaust air-fuel ratio is determined to be rich based on the output of the oxygen sensor on the downstream side of the exhaust purification catalyst at a high load in the air-fuel ratio feedback control region, a skip amount is further generated. The update of the rich skip amount generated by the means is stopped by the skip amount update stop means. In this manner, the rich skip amount is suppressed from being corrected to the air-fuel ratio feedback correction coefficient to the lean side, and the effect of adding the skip amount of the air-fuel ratio feedback correction coefficient to the rich side by the high load correction coefficient is corrected. Is ensured. As a result, harmful substances in the exhaust gas can be reliably and efficiently purified.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of an air-fuel ratio control apparatus for an internal combustion engine according to the present invention will be described with reference to the drawings.

As shown in FIG. 1, the air-fuel ratio control device of this embodiment has an exhaust purification catalyst 2 on an exhaust passage 1. The exhaust purification catalyst 2 is a three-way catalyst, which oxidizes and purifies hydrocarbons HC and carbon monoxide CO, which are unburned fuels in the exhaust gas, and purifies by reducing nitrogen oxides NOx in the exhaust gas. Let it. Then, air-fuel ratio feedback control is performed so that the air-fuel ratio of the internal combustion engine is the stoichiometric air-fuel ratio so that the oxidation of hydrocarbon HC and carbon monoxide CO and the reduction of nitrogen oxide NOx are performed in a well-balanced manner.

The upstream side and the downstream side of the exhaust purification catalyst 2 include:
An upstream oxygen sensor 3 and a downstream oxygen sensor 4 for detecting whether the air-fuel ratio of the exhaust gas on the exhaust passage is rich or lean by detecting the oxygen concentration in the exhaust gas.
Are mounted as air-fuel ratio sensors. As the air-fuel ratio sensor, a sensor other than the above-described oxygen sensor, for example, a limiting current type oxygen sensor capable of linearly measuring the air-fuel ratio may be used.

Here, the air-fuel ratio of the exhaust gas (exhaust air-fuel ratio)
Rich is equivalent to exhaust gas exhausted from the combustion chamber when the internal combustion engine is burned at an air-fuel ratio richer than the stoichiometric air-fuel ratio (called rich air-fuel ratio) with little oxygen in the exhaust gas. Point to Similarly, the term “lean exhaust air-fuel ratio” means that the exhaust gas contains oxygen and the combustion chamber is burned when the internal combustion engine is burned at an air-fuel ratio leaner than the stoichiometric air-fuel ratio (called lean air-fuel ratio). Refers to a case corresponding to exhaust gas exhausted from the

On the intake passage 5, an air flow meter 6 for detecting an intake air amount and a throttle valve 7 for adjusting the intake air amount are provided. Throttle valve 7
Is linked with an accelerator pedal 8 operated by the driver, and the accelerator opening of the accelerator pedal 8 is detected by an accelerator position sensor 9. The opening of the throttle valve 7 is detected by a throttle position sensor 10.

An injector 11 for injecting fuel into the intake passage 5 is disposed near the cylinder 12 of the intake passage 5. Above the cylinder 12, a spark plug 13 for igniting an air-fuel mixture in the cylinder 12, an intake valve 14 for opening and closing between the intake passage 5 and the cylinder 12, and an exhaust valve 15 for opening and closing between the exhaust passage 1 and the cylinder 12. Are also provided.

The position of the piston 16 is detected by a crank position sensor 17. In conjunction with this, the ignition timing of the ignition plug 13 and the intake and exhaust valves 14,
15 is controlled. The crank position sensor 17 can detect not only the position of the piston 16 but also the rotation speed of an engine which is an internal combustion engine.

The two oxygen sensors 3 and 4, the air flow meter 6, the accelerator position sensor 9, the throttle position sensor 10, the injector 11, the spark plug 13 and the crank position sensor 17 are connected to an electronic control unit (ECU) 18. The engine is ECU1
8 is comprehensively controlled. The ECU 18 has a CPU, ROM, R
It is a microcomputer composed of an AM or the like, and also has a backup RAM in which stored contents are retained without being erased by a battery even after an ignition key is turned off.

The ECU 18 functions together with the oxygen sensors 3 and 4 and the like as a skip amount generating means for generating a skip amount of the air-fuel ratio feedback correction coefficient FAF, and also performs an air-fuel ratio feedback correction for generating the air-fuel ratio feedback correction coefficient FAF itself. The correction coefficient generation means also functions as a high-load correction coefficient generation means for correcting the above-described rich skip amount when the load is high in the air-fuel ratio feedback region, and also functions as a skip amount update stop means for stopping the above-described update of the skip amount. .

The ECU 18 is provided with the air flow meter 6.
The basic fuel injection amount TP determined from the intake air amount detected by the engine and the engine speed detected by the crank position sensor 17 is corrected by the air-fuel ratio feedback control based on the outputs of the oxygen sensors 3 and 4 to correct the air-fuel ratio. Also controls the air-fuel ratio. Note that the basic fuel injection amount TP may be determined from the accelerator opening detected by the accelerator position sensor 9 and the engine speed detected by the crank position sensor 17. Further, the intake air amount can also be detected from the intake pipe negative pressure detected by a vacuum sensor provided on the intake passage 5 instead of the air flow meter 6.

Next, the air-fuel ratio feedback control performed by the above-described air-fuel ratio control device will be described.

The air-fuel ratio of the internal combustion engine is controlled by adjusting the fuel injection amount TAU. When the engine, which is the internal combustion engine, starts and the engine speed exceeds a predetermined value, the fuel injection amount TAU is calculated by the following equation (1). TAU = TP × FAF × α + β (1) Here, the basic fuel injection amount TP is determined based on the intake air amount detected by the air flow meter 6 and the engine speed detected by the crank position sensor 17. The basic fuel injection amount TP is corrected by the air-fuel ratio feedback correction coefficient FAF and other correction coefficients α and β to finally obtain the fuel injection amount TAU. The basic fuel injection amount TP is stored in the ROM in the ECU 18 as a map. The air-fuel ratio feedback control is performed by the above-described air-fuel ratio feedback correction coefficient FAF so that a desired air-fuel ratio is obtained.

FIG. 2 shows a flowchart of a routine for calculating the air-fuel ratio feedback correction coefficient FAF. This routine is stored in the ROM in the ECU 18, and is repeatedly executed at regular intervals (for example, every several milliseconds).

First, it is determined whether an execution condition for performing the air-fuel ratio feedback control is satisfied (step 1).
00). This execution condition is that the oxygen sensors 3 and 4 are activated (the oxygen sensors 3 and 4, which are air-fuel ratio sensors, must reach a predetermined activation temperature in order to exhibit their functions). And that the warm-up operation has been completed. If the execution condition of the air-fuel ratio feedback control is not satisfied, that is, if step 100 is denied, the air-fuel ratio feedback control is not performed.
Is set to 1.0, and this routine is ended once. If the air-fuel ratio feedback correction coefficient FAF is 1.0, the basic fuel injection amount TP is not corrected by the air-fuel ratio feedback correction coefficient FAF.

If the execution condition of the air-fuel ratio feedback control is satisfied, that is, if step 100 is affirmed, the output of the upstream oxygen sensor 3 is output to perform the air-fuel ratio feedback control by the air-fuel ratio feedback correction coefficient FAF. Is read, and an upstream air-fuel ratio flag F1 is generated based on the detected signal.

In step 101 following step 100, the upstream air-fuel ratio flag F1 is inverted (F1 = 0 → 1 or
It is determined whether or not it is immediately after (F1 = 1 → 0). Reversal of the upstream air-fuel ratio flag F1 indicates that the exhaust air-fuel ratio has changed from rich to lean or from lean to rich. If it is determined in step 101 that the upstream air-fuel ratio flag F1 has been inverted, then,
It is determined whether or not the operating state of the internal combustion engine is in a high load region within the air-fuel ratio feedback region (step 10).
2). Whether or not the operation state of the internal combustion engine is high load is determined by the intake air amount GA. The intake air amount GA is detected by the air flow meter 6, and the intake air amount GA
Is greater than a predetermined value (for example, 16 g / sec in this case), it is determined that the operation range of the internal combustion engine is a high load.
Note that the predetermined value of the intake air amount GA for determining whether or not the operation range of the internal combustion engine is under a high load may vary depending on the exhaust amount.

In the following, first, when Step 101 is denied, and when Step 102 is denied after Step 101 is affirmed (ie, when the load is not in the high load range in the air-fuel ratio feedback range), Generation of air-fuel ratio feedback correction coefficient FAF (steps 107 to 107)
112) will be described. Thereafter, the generation of the air-fuel ratio feedback correction coefficient FAF (steps 104 to 106) when step 102 is affirmed (that is, in the case of the high load region within the air-fuel ratio feedback region) will be described.

The output of the oxygen sensors 3 and 4 and the air-fuel ratio flags F1 and F2 based on the outputs of the oxygen sensors 3 and 4, based on the air-fuel ratio flags F1 and F2 when the load is not in the high-load region in the air-fuel ratio feedback region. FIG. 3 shows a timing chart of the rich skip amount RS and the air-fuel ratio feedback correction coefficient FAF generated as described above. In the timing chart shown in FIG. 3, the vertical magnification of the broken line indicating the rich skip amount RS and the broken line indicating the air-fuel ratio feedback correction coefficient FAF do not match.

The exhaust purification catalyst 2 purifies harmful substances in exhaust gas, and the exhaust purification catalyst 2 has a property of storing oxygen (O ₂ storage function). The inversion cycle of the output of the side oxygen sensor 4 is longer than the inversion cycle of the output of the upstream oxygen sensor 3. Here, for the sake of explanation, the inversion cycle of the rich skip amount RS is shown to be approximately four times the inversion cycle of the air-fuel ratio feedback correction coefficient FAF. The cycle may be tens to hundreds times the reversal cycle of the air-fuel ratio feedback correction coefficient FAF.

As shown in the upper part of FIG. 3, based on the output of the downstream oxygen sensor 4, it is determined whether the exhaust air-fuel ratio on the downstream side of the exhaust purification catalyst 2 is rich or lean. A fuel ratio flag F2 is generated. The downstream air-fuel ratio flag F2 is set to 1 when the exhaust air-fuel ratio downstream of the exhaust purification catalyst 2 is rich, and is set to 0 when the exhaust air-fuel ratio is lean.

While the downstream air-fuel ratio flag F2 is 0, the exhaust air-fuel ratio on the downstream side of the exhaust purification catalyst 2 is lean, so that the air-fuel ratio feedback is performed to make the air-fuel ratio of the internal combustion engine rich. Rich skip amount R of correction coefficient FAF
Increase S gradually. Conversely, the downstream air-fuel ratio flag F2
Is 1, the exhaust air-fuel ratio on the downstream side of the exhaust purification catalyst 2 is rich. Therefore, the rich skip amount RS of the air-fuel ratio feedback correction coefficient FAF is gradually reduced so that the air-fuel ratio of the internal combustion engine becomes lean. Let it.

When the downstream air-fuel ratio flag F2 is inverted from 1 to 0, it means that the exhaust air-fuel ratio on the downstream side of the exhaust purification catalyst 2 has changed from rich to lean. , The rich skip amount RS is increased in a skip manner. Conversely, when the downstream air-fuel ratio flag F2 is inverted from 0 to 1, it means that the exhaust air-fuel ratio on the downstream side of the exhaust purification catalyst 2 has changed from lean to rich. , The rich skip amount RS is increased in a skip manner. The reason why the rich skip amount RS is changed in a skip manner is to improve responsiveness. As described above, the rich skip amount RS may not be changed in a skip manner.

In this case, the reference value of the rich skip amount RS is 0.05 [5%], and the lean skip amount is
(0.1-RS) [10% -RS]. Thus, the sum of the rich skip amount RS and the lean skip amount (0.1-RS) is constant.
(0.1 [10%]), controllability can be improved.

As shown in the lower part of FIG. 3, based on the output of the upstream oxygen sensor 3, the exhaust air-fuel ratio on the upstream side of the exhaust purification catalyst 2 (ie, the air-fuel ratio of the exhaust gas immediately after combustion of the internal combustion engine). An upstream air-fuel ratio flag F1 that determines whether is rich or lean is generated. Here, a case will be described in which a signal obtained by directly A / D converting the output of the upstream oxygen sensor 3 is directly used as the upstream air-fuel ratio flag F1. The upstream air-fuel ratio flag F1 is set to 1 when the exhaust air-fuel ratio on the upstream side of the exhaust purification catalyst 2 is rich, and is set to 0 when the exhaust air-fuel ratio is lean.

While the upstream air-fuel ratio flag F1 is 0 (that is, in step 101, the upstream air-fuel ratio flag F1
Is determined not to be inverted, and while it is determined in step 110 that the upstream air-fuel ratio flag F1 is 0)
Since the internal combustion engine is operated at a lean air-fuel ratio, the air-fuel ratio feedback correction coefficient FAF is gradually increased at a constant increase KIR in order to make the air-fuel ratio of the internal combustion engine rich (step 111).

Conversely, while the upstream air-fuel ratio flag F1 is 1 (that is, it is determined in step 101 that the upstream air-fuel ratio flag F1 has not been inverted, and in step 110, the upstream air-fuel ratio flag F1 is not changed). While it is determined that it is not 0),
Since the internal combustion engine is operated at the rich air-fuel ratio, the air-fuel ratio feedback correction coefficient FAF is gradually reduced at a constant decrease KIL in order to make the air-fuel ratio of the internal combustion engine lean (step 112).

When the upstream air-fuel ratio flag F1 is inverted from 1 to 0 (that is, when it is determined in step 101 that the upstream air-fuel ratio flag F1 is inverted and step 102 is denied, then in step 107, the upstream air-fuel ratio flag F1 is inverted). When the side air-fuel ratio flag F1 is determined to be 0), the air-fuel ratio of the internal combustion engine has changed from a rich air-fuel ratio to a lean air-fuel ratio. The air-fuel ratio feedback correction coefficient FAF is skippedly increased using the rich skip amount RS at that time (see the case where the rich skip amount RS = RS1 shown in FIG. 3) (step 10).
8).

On the contrary, when the upstream air-fuel ratio flag F1 is changed from 0 to 1
(Ie, after it is determined in step 101 that the upstream air-fuel ratio flag F1 has been reversed and step 102 is denied, in step 107, the upstream air-fuel ratio flag F1 becomes 0).
Is not the case), since the air-fuel ratio of the internal combustion engine has changed from a lean air-fuel ratio to a rich air-fuel ratio,
Lean skip amount (0.1-RS) based on the rich skip amount RS at that time to make the air-fuel ratio of the internal combustion engine leaner
Is used to skip the air-fuel ratio feedback correction coefficient FAF in a skip manner (see FIG. 3, the rich skip amount RS = R
(See the case of S2) (Step 109). Immediately after the upstream air-fuel ratio flag F1 is inverted, the air-fuel ratio feedback correction coefficient
The reason why the FAF is changed in a skip manner is to improve the responsiveness of the air-fuel ratio control.

On the other hand, if step 102 is affirmed,
That is, in the case of the high load region in the air-fuel ratio feedback region, the high-load correction coefficient KRS for adding and correcting the skip amount of the air-fuel ratio feedback correction coefficient FAF so that the air-fuel ratio feedback correction coefficient FAF is on the rich side is calculated. (Step 103).

At a high load, as described above, the amount of intake air (the air contains nitrogen N ₂ ) increases and the combustion temperature rises. The amount increases. At this time, by setting the air-fuel ratio of the internal combustion engine to the rich side (increasing the fuel injection amount), the combustion temperature is reduced, and the reducing agent serving as a reducing agent for reducing and purifying the nitrogen oxides NOx on the exhaust purification catalyst 2 is reduced. Hydrocarbon HC and carbon monoxide CO, which are fuels, can be supplied. Therefore, harmful substances in the exhaust gas can be reliably purified.

High load correction coefficient KRS in step 103
FIG. 4 is a flowchart of a subroutine relating to calculation of
It is shown in (a). As shown in FIG. 4A, the high load correction coefficient KRS is calculated from a map stored in the ROM in the ECU 18 based on the intake air amount GA (step 200).
This map is shown in FIG. As shown in FIG. 4B, the high load correction coefficient KRS increases as the intake air amount GA increases. Further, as the map, it is also possible to use a map that increases in a stepwise manner as shown in FIG. In the map shown in FIG. 4C, when the intake air amount GA is 16 <GA ≦ 20 (g / sec), the high load correction coefficient KRS is 0.005 [0.5%], and 20 <GA ≦ 24 (g). / sec), the high load correction coefficient KRS is 0.010 [1.0%], 24 <GA ≤ 28 (g
/ sec), the high load correction coefficient KRS is set to 0.015 [1.5%].

FIG. 5 shows a flowchart of the above-described routine for updating the rich skip amount RS. The rich skip amount RS indicates that the operation state of the internal combustion engine is high and the downstream oxygen sensor 4 When the exhaust air-fuel ratio on the downstream side of the exhaust purification catalyst 2 is rich (ie, when the downstream air-fuel ratio flag F2 is not 0), the update of the rich skip amount RS is stopped (ie, the operating state of the internal combustion engine). Is kept at the rich skip amount RS when the load becomes high.)

Referring to the flowchart shown in FIG. 5, first, it is determined whether execution conditions such as whether the engine coolant temperature is equal to or higher than a predetermined temperature, whether the downstream oxygen sensor is activated, and the like are satisfied. Is determined (Step 30)
0). If the execution condition is not satisfied, this routine ends. If the execution condition is satisfied, as in step 102 of the flowchart shown in FIG. 2, whether the operating state of the internal combustion engine is a high load state is determined by the intake air amount GA.
(Step 301).

If the operation state of the internal combustion engine is not a high load state, that is, if the intake air amount GA is 16 g / sec or less, step 30
If 1 is denied, the rich skip amount RS is updated as usual (step 303). On the other hand, when the operation state of the internal combustion engine is a high load state, that is, when the intake air amount GA is 16
If g / sec is exceeded and step 301 is affirmed, it is determined whether or not the downstream air-fuel ratio flag F2 is 0 (step 302).

When the downstream air-fuel ratio flag F2 is 0, that is, when the air-fuel ratio downstream of the exhaust purification catalyst 2 is lean and step 302 is affirmed, the rich skip amount RS is updated as usual ( Step 303). On the other hand, if the downstream air-fuel ratio flag F2 is 1, that is, if the air-fuel ratio downstream of the exhaust purification catalyst 2 is rich and step 302 is denied, the update of the rich skip amount RS is stopped (step 304).

In the flowchart shown in FIG.
It is determined that the upstream air-fuel ratio flag F1 has been inverted (step 10).
1 is affirmed), and it is determined that the operating state of the internal combustion engine is in the high load region within the air-fuel ratio feedback region (step 102 is affirmative), and the high load correction coefficient KRS is determined.
Is calculated (step 103), it is determined whether or not the upstream air-fuel ratio flag F1 is 0 (step 10).
4).

If the upstream air-fuel ratio flag F1 is 0 in step 104, that is, if the upstream air-fuel ratio flag F1 is 1
From 0 to 0 when the air-fuel ratio of the internal combustion engine has changed from a rich air-fuel ratio to a lean air-fuel ratio. The air-fuel ratio feedback correction coefficient FAF is skipped by the sum of the rich skip amount RS (step 105).

If the upstream air-fuel ratio flag F1 is 1 in step 104, that is, if the upstream air-fuel ratio flag F1 is 0
When the air-fuel ratio of the internal combustion engine changes from lean air-fuel ratio to rich air-fuel ratio when the air-fuel ratio of the internal combustion engine changes from 1 to 1, the lean skip amount is set so that the air-fuel ratio of the internal combustion engine becomes lean.
The air-fuel ratio feedback correction coefficient FAF is reduced in a skip manner by the amount obtained by subtracting the high load correction coefficient KRS from (1.0-RS) (step 106). Steps 105 and 1
In 06, when the downstream air-fuel ratio flag F2 is 1, the update is stopped and the rich skip amount RS held is used.

That is, when the load is high, the skip amount (the rich skip amount RS and the lean skip amount (0.1-RS)) of the air-fuel ratio feedback correction coefficient FAF is always corrected to the rich side by the high load correction coefficient KRS. Is done. For this reason, even if the engine operation state becomes high load in the air-fuel ratio feedback region and the emission amount of nitrogen oxide NOx increases, the air-fuel ratio of the internal combustion engine is corrected to the rich side by the high load correction coefficient KRS. Therefore, it is possible to reliably purify nitrogen oxides NOx while purifying hydrocarbons HC and carbon monoxide CO.

Further, while the downstream air-fuel ratio flag F2 is 1, the updating of the rich skip amount RS is stopped to prevent the rich skip amount RS from being reduced, and the air-fuel ratio feedback is also performed from this point. The correction coefficient FAF is corrected to the rich side. For this reason, by suppressing the rich skip amount RS from being reduced, the air-fuel ratio of the internal combustion engine is corrected to the rich side, and the nitrogen oxides NOx are reliably removed while purifying the hydrocarbon HC and the carbon monoxide CO. Can be purified. If the update of the rich skip amount RS is not stopped, even if the air-fuel ratio of the internal combustion engine is corrected to the rich side by the high load correction coefficient KRS, the rich skip amount RS becomes too small and the nitrogen oxide NOx cannot be sufficiently purified. There are cases.

When the output of the downstream oxygen sensor 4 is lean, that is, when the downstream air-fuel ratio flag F2 is 0,
Since the rich skip amount RS is updated so as to increase the rich skip amount RS, the air-fuel ratio feedback correction coefficient FAF is reliably corrected to the rich side without stopping the update of the rich skip amount RS. Therefore, when the downstream air-fuel ratio flag F2 is 0, there is no need to stop updating the rich skip amount RS.

As described above, only when the load is high, the air-fuel ratio feedback correction coefficient FAF is added by stopping the updating of the high load correction coefficient KRS and the rich skip amount RS. Correction factor at load
If the addition to the rich side by the KRS is stopped and the update of the rich skip amount RS is restarted, the control can be promptly shifted to the light-load air-fuel ratio feedback control.

Further, as the exhaust gas temperature (combustion temperature) is higher and the exhaust air-fuel ratio is leaner, the deterioration of the exhaust purification catalyst 2 is accelerated.
The air-fuel ratio feedback correction coefficient FAF is corrected to the rich side by stopping the update of the rich skip amount RS and the rich skip amount RS, and the exhaust gas temperature is lowered by increasing the fuel amount, and the exhaust air-fuel ratio is set to the rich side to suppress the deterioration of the exhaust purification catalyst 2. You can also. This is because the exhaust purification catalyst 2 is likely to deteriorate when the temperature of the exhaust gas is high and the exhaust air-fuel ratio is lean.

The air-fuel ratio feedback correction coefficient FAF
Has a lower limit of 0.8 and an upper limit of 1.2, and the steps 105, 106, 108, 109, 111, 112
If the generated FAF exceeds the above-described limit value, the limit value is corrected in steps 113 to 116.

The air-fuel ratio control device for an internal combustion engine according to the present invention is not limited to the above-described embodiment. For example, in the above-described embodiment, the output of the upstream oxygen sensor 3 is directly reflected on the upstream air-fuel ratio flag F1, but after the exhaust air-fuel ratio is inverted from rich to lean using the delay counter CDLY, the lean The upstream air-fuel ratio flag F1 is inverted so that the upstream air-fuel ratio flag F1 is inverted when the state has elapsed for a predetermined time (or after the rich state has been inverted for a predetermined time after lean-to-rich inversion). ). In this way, when the exhaust air-fuel ratio repeatedly reverses in a short time, it is possible to prevent the air-fuel ratio control from becoming rough.

The generation of the upstream air-fuel ratio flag F1 using the delay counter CDLY will be briefly described. FIG. 6 shows a flow chart in this case. This flow chart shows steps 100 and 101 in the routine for calculating the air-fuel ratio feedback correction coefficient FAF shown in FIG.
What should be done is between.

First, the output of the upstream oxygen sensor 3 is read (step 400), and it is determined whether or not this output indicates lean (step 401). If the output of the upstream oxygen sensor 3 indicates lean, that is, if the result of step 401 is affirmative, it is determined whether or not the delay counter CDLY is positive (step 40).
2). If the delay counter CDLY is positive, that is, if step 402 is affirmed, the delay counter CDLY
LY is reset to 0 (step 403). Step 4
When the result of step 02 is negative, or after the delay counter CDLY is reset to 0 in step 403, the delay counter CDLY is reduced by 1 (step 404).

If the delay counter CDLY after the processing of step 404 becomes smaller than the predetermined delay counter value TDL (negative number) in the process of repeatedly performing the routine for calculating the air-fuel ratio feedback correction coefficient FAF, step 404 is performed. If it is determined in step 405 following the above, the delay counter CDLY is set to the delay counter value TDL,
Here, the upstream air-fuel ratio flag F1 is set to 0 for the first time. In addition,
If step 405 is denied, the process directly exits the flowchart shown in FIG.

In step 401, when the output of the upstream oxygen sensor 3 does not indicate lean, that is, when step 401 is denied, almost the same processing is performed. It is determined whether or not the delay counter CDLY is negative (step 408). If the delay counter CDLY is negative, the delay counter CDLY is reset to 0 (step 409). When step 408 is denied, or in step 410, the delay counter CDLY is set to 0.
After that, the delay counter CDLY is incremented by one (step 410).

If the delay counter CDLY after the processing of step 410 becomes larger than the predetermined delay counter value TDR (positive number) in the process of repeatedly performing the routine for calculating the air-fuel ratio feedback correction coefficient FAF, step 410 If it is determined in step 411 following the above, the delay counter CDLY is set to the delay counter value TDR,
Here, the upstream air-fuel ratio flag F1 is set to 1 for the first time. In addition,
If step 411 is denied, the process directly exits the flowchart shown in FIG.

FIG. 7 exemplifies changes in the output value of the upstream oxygen sensor 3, the delay counter CDLY, the upstream air-fuel ratio flag F1, and the air-fuel ratio feedback correction coefficient FAF in the air-fuel ratio feedback control using the delay counter CDLY. . If the upstream air-fuel ratio flag F1 is generated through the processing of steps 400 to 413 shown in FIG. 6, after the output of the upstream oxygen sensor 3 is inverted as shown in FIG.
If this state does not continue for a certain period, the upstream air-fuel ratio flag F1
Is not inverted. Therefore, even if the output of the upstream oxygen sensor 3 outputs a spike-like rich (or lean) signal, it is possible to prevent the upstream air-fuel ratio flag F1 from being frequently inverted. It is possible to prevent the air-fuel ratio feedback correction coefficient FAF from becoming rough.

[0060]

The air-fuel ratio control apparatus for an internal combustion engine according to the present invention
An air-fuel ratio sensor is provided on the upstream and downstream sides of the exhaust purification catalyst, and a skip amount is generated by a skip amount generation unit based on an output of the downstream air-fuel ratio sensor, and a skip amount is generated by an air-fuel ratio feedback correction coefficient generation unit. The air-fuel ratio feedback correction coefficient is generated based on the output of the upstream-side air-fuel ratio sensor. At this time, when the internal combustion engine is operating under a high load in the air-fuel ratio feedback region, the high load correction coefficient generation means generates a high load correction coefficient for adding and correcting the rich skip amount, and the skip amount update stop means, During high load operation and when the output of the downstream air-fuel ratio sensor is rich, updating of the rich skip amount is stopped. For this reason, even if the engine operating state becomes a high load in the air-fuel ratio feedback region and the emission amount of nitrogen oxide NOx increases, the air-fuel ratio of the internal combustion engine is corrected to the rich side, and the nitrogen oxide NOx is reliably reduced. Can be purified.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an embodiment of an air-fuel ratio control device for an internal combustion engine according to the present invention.

FIG. 2 is a flowchart showing a process of calculating an air-fuel ratio feedback correction coefficient FAF by the device shown in FIG. 1;

FIG. 3 shows a rich skip amount RS and an air-fuel ratio feedback correction coefficient during the air-fuel ratio feedback control shown in FIG. 2;
6 is a timing chart showing FAF and the like.

FIG. 4A is a flowchart showing a routine for calculating a high load correction coefficient KRS by the apparatus shown in FIG. 1;
(b) and (c) are maps showing the relationship between the intake air amount GA and the high load correction coefficient KRS.

FIG. 5 is a flowchart showing a routine for updating a rich skip amount RS by the device shown in FIG. 1;

FIG. 6 shows a delay counter CD in the device shown in FIG.
5 is a flowchart when determining an upstream air-fuel ratio flag F1 using LY.

7 is a timing chart showing an output value of an upstream air-fuel ratio sensor, a delay counter CDLY, an upstream air-fuel ratio flag F1, and an air-fuel ratio feedback correction coefficient FAF during the air-fuel ratio feedback control according to the flowchart shown in FIG.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Exhaust passage, 2 ... Exhaust purification catalyst, 3 ... Upstream oxygen sensor (air-fuel ratio sensor), 4 ... Downstream oxygen sensor (air-fuel ratio sensor), 18 ... ECU.

Claims (1)

[Claims] An exhaust purification catalyst provided on an exhaust passage of the internal combustion engine; an upstream air-fuel ratio sensor provided upstream of the exhaust purification catalyst for detecting an air-fuel ratio of the internal combustion engine; A downstream air-fuel ratio sensor that is provided downstream of the catalyst and detects an air-fuel ratio of the internal combustion engine.Based on an output of the downstream air-fuel ratio sensor, a rich skip amount and a lean skip amount of an air-fuel ratio feedback correction coefficient. An air-fuel ratio feedback correction coefficient generation unit that generates an air-fuel ratio feedback correction coefficient based on the skip amount generated by the skip amount generation unit and an output of the upstream air-fuel ratio sensor; A high load correction unit for adding and correcting the rich skip amount generated by the skip amount generation means during a high load operation of the internal combustion engine. A high-load correction coefficient generating unit that generates the rich skip amount by the rich skip amount generating unit during the high-load operation of the internal combustion engine and when the output of the downstream air-fuel ratio sensor is rich. An air-fuel ratio control device for an internal combustion engine, comprising: a skip amount update stop unit that stops updating.